Changed recommended PostgreSQL settings for increased safety

Maybe I was over-agressive in my initial recommendation to turn
off fsync. Just turning off synchronous commits should be a
reasonable compromise between safety and performance.
Change some UNIONs to UNION ALL where it can't affect things

The timetables won't have multiple rows for the same station/time
and train_uid so changing the UNIONs to UNION ALLs saves a
check for distinct rows.